import java.util.*;

public class ListNode {
  int val;
  ListNode next = null;

  public ListNode(int val) {
    this.val = val;
  }
}

class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * param pHead1 ListNode类 the head node
     * @return ListNode类
     */

    ListNode merge(ListNode pHead1, ListNode pHead2) {
        if(pHead1 == null)
            return pHead2;
        if(pHead2 == null)
            return pHead1;
        ListNode head = new ListNode(0);
        ListNode cur = head;
        while(pHead1 != null && pHead2 != null){
            if(pHead1.val <= pHead2.val){
                cur.next = pHead1;
                pHead1 = pHead1.next;
            }else{
                cur.next = pHead2;
                pHead2 = pHead2.next;
            }
            cur = cur.next;
        }
        if(pHead1 != null)
            cur.next = pHead1;
        else
            cur.next = pHead2;
        return head.next;
    }

    public ListNode sortInList (ListNode head) {
        // write code here

        if(head == null || head.next == null)
            return head;
        ListNode left = head;
        ListNode mid = head.next;
        ListNode right = head.next.next;
        while(right != null && right.next != null){
            left = left.next;
            mid = mid.next;
            right = right.next.next;
        }
        left.next = null;

        return merge(sortInList(head), sortInList(mid));
    }
}